1. Field of the Invention
The present invention relates to a file and/or folder management technique.
2. Description of the Related Art
Distributed data management systems are recently implemented, in which a plurality of apparatuses connected via a network manage data virtually by a single system in cooperation with each other.
For example, independently of the local file system of each apparatus, a virtual distributed file system is provided as an integrated system for the apparatuses (Japanese Patent Laid-Open No. 2001-051890). A system of this type has correlation data between a path to actually save data on a local file system and a path on the virtual distributed file system. A client accesses data by using the path on the virtual distributed file system. This provides a virtual distributed file system that conceals local file systems and unifies a plurality of apparatuses.
The virtual single system has the same tree structure of folders as in the local file system. The system has a root folder on top. Subfolders and contents are saved under the root folder. Each subfolder also has its subfolders and contents. The folder groups form a tree structure. The contents are saved in one folder. A folder that saves subfolders and contents is called a parent folder.
The virtual distributed file system is operable by a plurality of apparatuses. The plurality of apparatuses may parallelly execute conflicting operations. To cause other apparatuses to share an execution result after a conflicting operation, the conflict needs to be solved, though this is a complex process. In many cases, parallel execution of conflicting operations is prevented by locking folders and contents. For example, to delete a folder and its subordinate data, the apparatus that executes this operation locks the folder and all the subordinate folders and contents. The folders and contents are deleted after they are locked. The remaining apparatuses cannot change the locked folders and contents. Hence, any conflicting operation can be prevented.
In the conventional distributed data management system, however, the folders and contents must be saved somewhere on the tree structure. If an operation would change the tree structure, the number of folders to be locked increases. Since the number of unchangeable folders that are already locked by other apparatuses increases, operations that are executable in parallel are limited. Especially when an apparatus is disconnected from the network and used offline, the lock period is long, and the problem becomes more conspicuous.
For example, if there is a possibility that an apparatus may delete a specific folder, the specific folder and its subordinate folders and contents are locked. In this case, another offline apparatus disconnected from the apparatus cannot change any arbitrary folder or content under the folder.